The present invention concerns a laminate material, a process for the production of a coated carrier material in web or panel form, and a use of a modified synthetic resin for the surface coating of a carrier material.
Laminate materials of the general kind set forth, for example in the form of so-called decorative high-pressure molded laminated sheets or boards (DIN 16926), plastic-coated, decorative wood fiber boards or panels (DIN 68751) or plastic-coated, decorative flat pressed boards or panels in accordance with DIN 68765 are put to wide uses in everyday activities. It is precisely chipboards which are surface-coated by means of plastic material that are a preferred material in particular for the furniture industry in order in that case to manufacture products which can be loaded in terms of resistance to scratching and abrasion and which thus can be used for example as kitchen furniture. Even more severe demands in terms of resistance and loading capacity of a surface occur for example in the case of coatings for floor materials.
It is known from the state of the art for coatings of that kind, in particular in foil or sheet form for subsequent lamination to a subjacent carrier material, to be produced in the form of paper or plastic foil or sheet, which are coated with a layer consisting of a liquid acrylate and which are subsequently hardened therethrough by electron beam or UV-hardening. Even if those known layers already afford a degree of surface hardness or scratch resistance which is often already sufficient for the uses outlined, the level of scratch resistance which can be achieved in that way however is often still not adequate, in particular for surfaces of an end product, which are subjected to a severe scratching loading. In addition, for example in the case of conventionally coated chipboards, it was possible to note the detrimental effect that, when the surface coating was still hot on a panel or board coated in the described manner, they already have a tendency to suffer from scratching due to individual chipboard particles when a plurality of boards or panels are stacked one upon the other so that in this casexe2x80x94particularly in the case of large-scale mass production and when high production speeds are involvedxe2x80x94the surface quality is detrimentally affected, in a manner which is visible to a customer and which therefore causes the customer concern; it is to be borne in mind that, in industrial production, a surface coating with foils or sheets is effected at web speeds above 100 m/min while coating wood carrier materials with foils or sheets coated in that way reaches speeds of up to 40 m/min.
Therefore the object of the present invention is to further develop a laminate material of the general kind set forth, in such a way that its coating is improved in terms of scratch resistance and/or resistance to abrasion, and in particular also the laminate material which is improved in that way can be produced at high production or web speeds. The invention also seeks to provide a production process for such a laminate material.
Advantageously an acrylic resin which is modified in accordance with the invention provides that the coating surface which can be achieved therewith, after radiation hardening, is markedly enhanced in comparison with the unmodified acrylate in terms of its scratch resistance when subjected to a scratching loading. That measurement in relation to scratch resistance is related to DIN 53799 with the procedure set forth therein in section 4.15 for ascertaining the characteristics involved in the case of a scratching loading.
In accordance with the invention production of the nanoparticles is effected starting from silicon dioxide in firm, finely divided form, of a particle size in the range of between 1 and 500 nm. A silicon dioxide of that kind is commercially available, for example as Aerosil(copyright) available from Degussa AG, Frankfurt, DE, or Cab-o-sil from Cabot Corp, Boston, Mass., USA.
The silicon particles have hydroxyl groups at their surface. Bonding of the side chains is effected by way of those hydroxyl groups by reaction to afford (MeO)x(Mexe2x80x94(CH2)nxe2x80x94(OCO)mxe2x80x94CR1xe2x95x90CH2)y and (MeO)xMe(CH2)nOCOCR1xe2x95x90CH2, wherein Me stands for Si or Al, x ranges from 1 to 3, m stands for 0 or 1, n ranges from 0 to 6, y ranges from 1 to 3, and R1 stands for H or CH3, and the free valences of Me are saturated by alkoxy residues, in the presence of strong acids such as sulfuric acid, phosphoric acid, methane sulfonic acid or P-toluene sulfonic acid. In general between 1 and 10% by weight of the strong acid is used, in relation to the amount of silicon dioxide. The reaction temperature is generally between 30 and 80xc2x0 C. After the reaction is concluded the strong acid is neutralised with a base. If the incorporation of (MeO)x is wanted, the reaction is conducted in the presence of the corresponding Me-alkoxy compound, for example tetramethoxysilane or Al-isopropylate.
In accordance with the invention moreover a substrate is not limited to the materials explicitly mentioned in DIN 53799, but basically in particular also papers and plastic foils or sheets (preferably in web form) are to be considered as such a substrate, which are then provided with a conventional coating thickness, in dependence on the desired purpose of use.
Any chemical compounds which are characterised by the general structures: 
and 
are to be taken as an acrylate which is modified by nano-scale silica, in accordance with an independent implementation of the invention, wherein (Sixe2x80x94Oxe2x80x94Si)k(OH)1 are nano-scale silica particles which are bound by way of Sixe2x80x94Oxe2x80x94Si and/or Sixe2x80x94Oxe2x80x94Al bindings to an acrylate and/or methacrylate functionality, and wherein 
functions as a spacer group.
In addition in accordance with the invention the radiation involved is any radiation which is suitable for beam-chemical hardening of the coating material, for example electron radiation or UV-radiation, wherein the hardening kinetics are suitably set by means of otherwise known measures, in the case of using an UV-radiating device for example by the suitable addition of photoinitiators.
In a manner which is advantageous according to the invention it is consequently possible to obtain a surface coating which in comparison with the unmodified acrylate usually has values in terms of scratch resistance which are at least 50% higher, without however the coating procedures or processes which are otherwise also to be used and which are suitable for mass production having to be modified or without them being adversely affected in terms of their efficiency. On the contrary the acrylate which is used in accordance with the invention and which is modified by polymerisable nanoparticles (NKMA) makes it possible to use the liquid modified coating material in a similar manner in particular on conventional coating apparatuses practically without conversion procedures being involved so that in addition adoption of the technology in accordance with the invention, from the manufacturing point of view, is favourable and involves little complication and expenditure.
Advantageous developments of the invention are described in the appendant claims.
Thus, the surface hardness which can be achieved in respect of the polymerised coating surface which is modified in accordance with the invention, besides DIN 53799, can additionally be characterised by significantly increased hardness values in accordance with DIN 55350 or Erichsen hardness testing (test bar 318).
Plastics foils or sheets which are to be coated in accordance with the invention preferably entail layer thicknesses of between 40 and 300 xcexcm while papers to be coated in accordance with the invention particularly preferably involve weights of between 30 and 90 g/m2. Depending on the respective purpose of use involved, particularly preferred layer thicknesses of the coating applied in accordance with the invention are between 10 and 200 xcexcm.
In accordance with a preferred development of the invention it is provided that, before the radiation hardening step, the coating surface is matted in photoinitiator-free state by UV-irradiation, in particular using wavelengths of 172 nm and 222 nm respectively. Thus it has been found to be advantageous that irradiation of the liquid modified acrylate coating with photons of the specified wavelengths (emitted by so-called excimer lamps) under inert gas produces a characteristic surface hardening and compacting effect which brings about a matting effect.
FIG. 1 is a diagram of the coating apparatus of the present invention.
Further advantages, features and details of the invention will be apparent from the description hereinafter of preferred embodiments and with reference to FIG. 1; FIG. 1 diagrammatically shows the structure of a possible coating apparatus for applying acrylates modified in accordance with the invention with additional UV-matting prior to an electron beam hardening step.